Electrical devices



c: .L u "1 1 5x nunlwu DUUIII 5 12 8502 ER 5 Q 412756 April 29, 1969GSJANES ETAL 3,441,756

ELECTRICAL DEVICES Filed April 5, 1965 Sheet of 3 GEORGE S. JANESRICHARD H. LEVY F l l INVENTOR.

Maw B MW WM 5 W ATTORNEYS.

April 29, 1969 G, 5, JAMES ET AL 3,441,756

ELECTRI CAL DEVICES Filed April 5, l965 Sheet 2 of 5 TO CURRENT 8: HIGHVOLTAGE SOURCE FIG. 2

GEORGE S.JANES' RICHARD H. LEVY INVENTOR,

I I m 7, FIG. 3 ,ATTORNEYS.

April 29, 1969 G. s. JANES ET AL 3,441,756

ELECTRICAL DEVICES Filed April 1955 Sheet of 3 GEORGE S. JANES RICHARDH. LEVY INVENTOR.

MM w WJMZ? ATTORNEYS United States Patent 3,441,756 ELECTRICAL DEVICESGeorge S. Janes, South Lincoln, and Richard H. Levy,

Boston, Mass., assignors to Avco Corporation, Cincinnati, Ohio, acorporation of Delaware Filed Apr. 5, 1965, Ser. No. 445,357 Int. Cl.H02k 45/00 US. Cl. 310-11 17 Claims ABSTRACT OF THE DISCLOSURE Thisinvention relates to electrical devices and more particularly to animproved construction for and method of operating crossed fieldelectronic devices having a geometry which permits the trajectories ofelectrons in the crossed electric and magnetic fields to close onthemselves.

Apparatus in accordance with the present invention may comprise anevacuated chamber having a geometry which permits the trajectory of anelectron in the chamber to close on itself in the presence of staticcrossed electric and magnetic fields, means for providing in the chambera magnetic field having a strength sufiicient to provide an electrongyro radius in the chamber that is small compared to the size of thechamber, means for varying the magnetic flux within the chamber andmeans for injecting a suflicient quantity of electrons into the chamberto produce an electric field. This electrostatically induced electricfield will generally be greater than the induced electric field producedby the time varying magnetic field.

The present invention resulted from our research on plasma acceleratorsoperating under conditions such that the electron gyro radius is smallcompared to the apparatus size which is in turn small compared to theion gyro radius, and on radiation shielding in space which uncovered anew single component domain of plasma physics containing a wide varietyof applications. The term 0 single component is used herein to describeplasma con ditions wherein the number density of electrons exceeds thenumber density of ions and neutrals to such an extent that the plasmamotion is controlled by magnetic and collective electrostatic forcesrather than by magnetic and collective inertial (or pressure) forces,i.e. e E /2 nkT or v where s is the permittivity of free space, E is acharacteristic electric field in volts per meter, n is a characteristicnumber density of electrons per cubic meter, k is Boltzmanns constant, Tis a typical temperature in degrees Kelvin, p is a typical mass densityin kilograms per cubic meter, and v is a typical streaming velocity inmeters per second. The presence of a large excess of charged particlesof one sign leads to strong electric fields. If the magnetic field B isstrong enough to make E/B less than the speed of light and the electrongyro radius smaller than the minimum significant apparatus dimension,then the charged particles will drift with average speed E/B in thedirection perpendicular to both E and B. In certain applications,however, e E 2 may be less than nkT or p1 In accordance with the presentinvention, the electrons 3,441,756 Patented Apr. 29, 1969 are providedby injecting them onto magnetic flux shells simultaneously with thecreation or variation of the magnetic field. Thus, if it is assumed thatthe electron motions are adiabatic, i.e., E+(v B)=0, the electrons canbe considered as being confined to flux shells. As used herein, the termflux shell has the following meaning: each magnetic field line can beconsidered an equipotential since the electrons can flow rapidly alongthe field lines to nullify any potential gradient that does develop. Theequipotential surfaces will in this case contain a family of magneticfield lines; such a family of magnetic field lines comprising anequipotential surface is called a flux shell. If the external magneticfield is changed slowly, such surfaces retain their identity, eventhough the value of the potential may change. The flux shells serve as avehicle for transporting electrons away from their point of origin, thuscreating strong electric fields. Since the electrons on a particularflux shell also retain their identity as a group, we can also refer toelectron shells. This concept, which is basic to the present inventionand which we call Inductive Charging, while in a sense analogous to thebetatron concept is distinguishable therefrom in that power input in thepresent invention is utilized to increase the potential energy of theindividual charged particles in an electric field While the betatronmerely increases the kinetic energy of individual charged particles.

It is an object of the present invention to provide by the use ofmagnetic fields electron shells which may serve as mobile andindestructible equipotential surfaces.

Another object of the present invention is to provide a high voltagegenerator.

Another object of the present invention is to permit the production ofhigh electrostatic energy densities in predetermined geometricconfigurations which may produce high power, short duration oscillationsin a manner analogous to pulsed lasers.

A still further object of the present invention is to provide apparatushaving an electron shell which constitutes a highly conductive surfaceas well as an energy source.

A further object of the present invention is to provide apparatuswherein a movable electron shell may form part of a tunable cavity and/or wave guide.

A still further object of the present invention is to permit thegeneration of ultra-high temperature electrostatically contained plasmawhich results in preferential ion heating and ion trapping. When an atomis ionized in crossed electric and magnetic fields, the electronacquires a perpendicular energy equal to the quantity where m is themass of an electron, while the ion can acquire a perpendicular energyequal to the quantity (E/B) (m /2) where m is the mass of the ion. Inthe case of deuterium, the deuteron, for example, can acquire more than3000 times more energy than the electron. Thus, if the electric field iscreated by a cloud of electrons which are magnetically trapped on theinterior axis of a hollow torus or mirror geometry in accordance with afeature of the present invention, the ions will be automatically trappedby the electrostatic field.

According to an embodiment of the present invention for providingultra-high temperature plasma, there is provided a high vacuum system oftubular geometry closed on itself and surrounded by a toroidal coilwhich can be energized in a short time, and electron gun means forinjecting electrons into the vacuum at velocities in excess of E/B.Electrons which are injected into the high vacuum system, while themagnetic field is rising, are trapped and transported inward away fromthe outer walls of the high vacuum system on contracting magnetic fluxshells. This results in the generation of a radial electric field whichin turn produces a region near the axis in which the electrostaticpotential is depressed. Thus, when a deuterium (or other gas) atom isionized in the aforementioned electron shell, the electron thus producedis trapped in the magnetic field while the relatively heavy ion istrapped by the electric field. Because of its greater mass, the ion canacquire a larger kinetic energy in this configuration than can theelectron. Thus, the device causes both the preferential heating of ionsand the trapping of ions.

According to another embodiment of the present invention for generatinga high DC electrostatic potential, there is provided a highly evacuatedtubular region defined at its inner and outer periphery by cylindricallyshaped electrically conductive walls, which serve as negative andpositive electrodes insulated one from another by electricallynonconductive circular end plates which define the ends of the tubularregion. Surrounding the tubular or annular region is a coil suppliedfrom any suitable DC source for creating in the annular region an axialDC magnetic field. Provided at the tubular axis of the region is aferrite core surrounded by a second coil coupled to a source of ACcurrent for varrying the total magnetic flux enclosed within and/or bythe tubular or annular region. Electron gun means carried by the innerelectrically conductive wall is provided for injecting electrons intothe annular region. The electrons which are injected from the electrongun means are carried to the outer wall on typical trajectories inaccordance with the present invention. This transport of charge(electrons) is driven by the changing magnetic flux and results in thegeneration of a high voltage DC potential between the electricallyconductive walls. The cyclic repetition of this transport of chargeresults in the production of high voltage DC power. This feature of thepresent invention incorporates into a single package both the secondarytransformer windings and the high voltage rectifiers which are normallyemployed in high voltage DC generators.

The novel features that are considered characteristic of the inventionare set forth in the appended claims; the invention itself, however,both as to its organization and method of operation, together withadditional objects and advantages thereof, will best be understood fromthe following description of a specific embodiment when read inconjunction with the accompanying drawings, in which:

FIGURE 1 is a schematic top view of a'DC generator in accordance withthe present invention;

FIGURE 2 shows details of the electron gun;

FIGURE 3 is a schematic of the electron gun circuit; and

FIGURE 4 is a schematic sectional view illustrating a modificatioinhaving a generally toroidal configuration for generatingelectrostatically contained 'high temperature plasma.

Referring now to FIGURE 1, there is shown, by way of example and not oflimitation, apparatus in accordance with the present invention forgenerating a high DC electrostatic potential. As shown in this figure,there is provided a highly evacuated annular region defined byelectrically nonconductive cylindrical side walls 11 and 12 and annularend walls 13 and 14, only end wall 13 being shown. The side walls andend walls may be comprised of any suitable electrically nonconductivematerial such as glass or a ceramic. Assuming that the axial dimensionof walls 11 and 13 is greater than their radial spacing, the latter isdeemed to be the minimum significant size of region 10.

The inner surface of the side walls 11 and '12 are coated with anelectrically conductive material such as silver, which form respectivelynegative and positive electrodes 15 and 16. These conductive layers aresufficiently thick to carry away any electrostatic surface chargesthereby maintaining the surface as a equipotential, but not so thick asto interfere with the passage of magnetic flux through the surfaceseparating adjacent radial regions. Disposed within the cylindricalspace defined by wall 12 is a ferrite core 17 surround by a coil 18which is coupled to an AC source of current 19. Coil 18 may be coupledto a DC source of current and pulsed by means of a conventionalthyratron circuit (not shown), if desired. In this case, the electrongun, designated generally by the number 20, should also be pulsed suchthat it is turned on just before or when coil 18 is pulsed.

Surrounding side wall 11 is a second coil 21 which is coupled to a DCsource of current 22.

Disposed within the annular region 10 is conventional electron gun meansfor injecting electrons into the annular region v10. A suitableconfiguration for the electron gun is shown in FIGURE 2. As best shownin FIG- U-RE 2, the electron gun may comprise an emitter 30 of tantalumor tungsten supported on two relatively rigid standoff leads 31 and 32.The accelerator 33, which may also be supported on a standofi lead 34grounded to electrode 16, may for example be comprised of a screen ofnickel or stainless steel plate having a large number of small holes topermit the passage of electrons through the accelerator from the emitter30. Directing attention now to FIGURE 3, there is shown a schematicdiagram for providing pulsed operation of the electron gun. As shown inFIGURE 3, the accelerator 33 is grounded. Emitter 30 is coupled across abattery 35 and series connected resistors 36 and 37. The output of aconventional thyratron circuit, designated generally by the number 38,is connected between resistors 36 and 37. Thus, it will be apparent thatwhen the thyratron fires, a negative 2000 volts will be appliedintermediate resistors 36 and 37 to actuate the electron gun.

Returning now to FIGURE 1, electrons which are injected into region 10from the electron gun 20 are carried to the outer electrode 15 ontypical trajectories 40 similar to that illustrated in FIGURE 1 inaccordance with the inductive charging concept of the present invention.This transport of charges or carrying of electrons to electrode 15 isdriven by the changing magnetic flux in region 10 and results in thegeneration of high voltage DC power which may be utilized by connectinga load across electrodes 15 and 16.

It should be noted that the apparatus shown in FIG- URE l incorporatesinto a single device both the secondary transformer windings and thehigh voltage rectifiers which are normally employed in high voltage DCgenerators. It is to be understood that the present invention, asapplied to apparatus for generating a high DC electrostatic potential,is not limited to that shown and described. Thus, for example, thedisclosed apparatus will operate without the ferrite core although atthe probable expense of a decrease in efficiency. Furthermore, the ACcoil 18 may be incorporated into or combined with the outer DC coil 21.The use of the ferrite core merely represents one way in which the fluxenclosed by the annular region can be varied thereby altering theequilibrium radius of the enclosing electron shells. Further, the roleof the outer and inner electrodes 15 and 16 may be interchanged bymounting the electron gun on the outer wall. Still further, if desired,axial electric fields and radial magnetic fields may be used. In thiscase, the end walls 13 and 14 must be silvered and serve as theelectrodes while the inner and outer cylindrical walls 11 and 12 serveas simple insulators. Also the wall carrying the electron gun may bemade up of a single cylinder of highly conducting material which issplit axially at one point, thereby allowing the magnetic flux to enterover a small portion of the total circumferential coordinates. In thisembodiment, the electron gun is located in the split.

It will now be appreciated that the moving magnetic field provided inregion 10 eliminates the necessity for example of the belt in a highvoltage Van de Graalf generator. Further, those skilled in the art willnow appreciate that the inductive charging concept of the presentlnvention may be utilized in the field of microwave corn municationssuch as, for example, by generating movable electron shells for theprovision of tunable cavities and/ or wave guides. Those skilled in theart will further appreciate that movable electron shells which functionas grids may be provided in accordance with the present invention andthat such grids are immune to the heating and erosion problems commonlyassociated with conventional metallic grids. Accordingly, a grid formedin accordance with the present invention may be used, for example, forthe acceleration of ions in space propulsion applications.

Attention is now directed to FIGURE 4 which shows a modification of thepresent invention having an essentially toroidal geometry for generatingan electrostatically contained high temperature plasma. The apparatusshown in FIGURE 4 comprises a toroidal region 45 defined by the innersurface of an electrically nonconductive tubular container 46 composedof an electrically nonconductive material such as glass or quartz.Surrounding the container is a multi-turn coil 47 coupled to a source ofcurrent 48 through a switch 49. Disposed within and carried by thecontainer 46 is an electron gun 50 of the type previously described forinjecting electrons into the toroidal region 45 at velocities in excessof E /B, where E,. is the radial electric field and B is thecircumferential magnetic field.

Pipe 51 and means 52 are provided for injecting a gas or ions such as,for example, deuterium ions, into region 45.

The injection of electrons into region 45 while the magnetic field Bproduced by the coil 47 is rising in region 45 results in these eectronsbeing trapped by the rising magnetic field and transferred into ortoward the center of region 45 on magnetic flux shells. Theaforementioned trapping and movement of electrons results in thegeneration of a radial electric field which, in turn, depresses theelectrostatic potential in the central portion of region 45. Neutralatoms (deuterium atoms) in or introduced into region 45 wi l be ionizedby the trapped electrons therein. The electrons produced by thisionization will in turn be trapped by the magnetic field while therelatively heavy ions will be trapped by the electric field. The ions ofcourse have a considerably greater mass than the eectrons and for thisreason can acquire a larger kinetic energy than the electrons. Thus, inthe apparatus of FIGURE 4, both the preferential heating of ions and thetrapping of ions occur simultaneously. For the embodiment shown inFIGURE 4, the minimum significant size of region 45 is deemed to be theradius about its I tubular axis. Ions can be injected into or providedin region 45 in several Ways. For example, deuterium gas may beintroduced through pipe 51 and means 52 and thereafter ionized in region45. In this case, means 52 may be a control valve. On the other hand, ifions rather than atoms are to be injected into region 45, means 52 maycomprise a conventional ion source wherein deuterium gas or the like isionized exterior of region 45 and only the ions are injected into region45. A suitable ion source for this purpose is disclosed in NationalAeronautics and Space Administration Technical Note D-585, January 1961,entitled An Ion Rocket with an Electron- Bombardment Ion Source, byHarold R. Kaufman.

Attention is directed to a previously suggested similarity inconfiguration of the chambers shown in FIGURE 1 and FIGURE 4. Thus,whereas the region of FIGURE 1 has been referred to as annular and theregion 45 of FIGURE 4 has been referred to as toroidal for clarity, itis to be noted that both of these regions may also be described as beingtubular in shape, the ends of tubular region 10 merely being closedwhereas tubular region 45 is endless in that it is closed on itself.Accordingly, tubular as used in the claims is generically descriptive ofboth regions. Since both regions may be defined as tubular, they ofcourse each have a tubular axis which in the case of region 10 isstraight and in the case of region 45 is ring-shaped.

The various features and advantages of the invention are thought to beclear from the foregoing description. Various other features andadvantages not specifically enumerated will undoubtedly occur to thoseversed in the art, as likewise will many variations and modifications ofthe preferred embodiment illustrated, all of which may be achievedwithout departing from the spirit and scope of the invention as definedby the following claims.

What is claimed is:

1. In an electrical device, the combination comprising:

(a) an evacuated chamber having at least one substantially cylindricalside wall defining at least in part a region which permits the motion ofan electron in said chamber to close on itself in the presence ofcrossed electric and magnetic fields;

(b) means for providing in said chamber a magnetic field substantiallyeverywhere parallel to said side wall and having a strength sufiicientto provide an electron gyro radius in said chamber that is smallcompared to the minimum significant size of said chamber;

(0) means for rapidly increasing the magnetic flux within said region;and

(d) means for injecting electrons into said chamber during said increaseof magnetic flux at a rate sufiicient that the induced electric field ofsaid electrons is greater than the electric field produced by variationof said magnetic field.

2. In an electrical device, the combination comprising:

(a) an evacuated chamber having at least one side wall substantiallycylindrical at substantially any given cross section defining at leastin part a region which permits the motion of an electron in said regionto close on itself in the presence of crossed electric and magneticfields:

(b) means for providing in said chamber a magnetic field substantiallyeverywhere parallel to said side wall and having a strength sufficientto provide an electron gyro radius in said chamber that is smallcompared to the minimum significant size of said chamber;

(c) means for rapidly increasing the magnetic flux within said region;and

(d) means for injecting electrons into said region during said increaseof magnetic fiux at a rate sufficient that the induced electric field ofsaid electrons is greater than the electric field produced by variationof said magnetic field, the mean direction of travel of said electronsbeing normal to both the induced electric field of said electrons andsaid magnetic field.

3. In an electrical device, the combination comprising:

,(a) an evacuated tubular chamber having a tubular axis wherein themotion of an electron in said chamber may close on itself about saidaxis in the presence of crossed electric and magnetic fields;

(b) means for providing in said chamber a magnetic field substantiallyeverywhere parallel to said tubular axis and having a strengthsufficient to provide an electron gyro radius in said chamber that issubstantially less than the minimum significant size of said chamber;

(c) means for rapidly increasing the magnetic flux within said chamberfrom a first value as low as zero to a second higher value; and

((1) means for injecting electrons into said chamber during saidincrease of magnetic flux at a rate sufficient that the induced electricfield of said electrons is greater than the electric field produced byvariation of said magnetic field, the means direction of travel of saidelectrons being about said tubular axis and normal to both the inducedelectric field of said electrons and said magnetic field.

4. In a direct current potential generator, the combination comprising:

(a) an evacuated annular chamber defined by two concentric cylindricalside walls and two circular end walls;

(b) means for providing in said chamber a magnetic field substantiallyeverywhere parallel to said side walls and having a strength sufficientto provide an electron gyro radius in said chamber that is smallcompared to the minimum significant size of said chamber;

(c) means for rapidly increasing the magnetic fiux within said chamber;and

(d) means for injecting electrons into said chamber during said increaseof magnetic flux at a rate sulficient that the induced electric field ofsaid electrons is greater than the electric field produced by variationof said magnetic field, the mean direction of travel of said electronsbeing normal to both the induced electric field of said electrons andmagnetic field.

5. In a direct current potential generator, the combination comprising:

(a) an evacuated annular chamber defined by two concentric cylindricalside walls and two circular end walls;

(b) means for providing in said chamber a magnetic field substantiallyeverywhere parallel to said side walls and having a strength sufficientto provide an electron gyro radius in said chamber that is smallcompared to the minimum significant size of said chamber;

(c) means for rapidly increasing the magnetic flux within said chamber;

((1) means for injecting electrons into said chamber during saidincrease of magnetic flux at a rate sulficient that the induced electricfield of said electrons is greater than the electric field produced byvariation of said magnetic field, the mean direction of travel of saidelectrons being normal to both the induced electric field of saidelectrons and magnetic field; and

(e) electrode means disposed on the surfaces of said side walls withinsaid chamber.

6. The combination as defined in claim 5 wherein said means forinjecting electrons into said chamber includes electron gun means.

7. The combination as defined in claim 5 wherein said means forproviding said magnetic field includes an electrical coil surroundingthe outermost side wall.

8. The combination as defined in claim 7 wherein said means for varyingthe magnetic flux within said chamber includes an electrical coil and aferrite core surrounded by the innermost side wall.

9. In a direct current potential generator, the combination comprising:

(a) an evacuated tubular chamber having a tubular axis and closed onitself;

(b) means including a coil surrounding substantially all of said chamberfor providing in said chamber a magnetic field substantially everywhereparallel to said tubular axis and having a strength sutficient toprovide an electron gyro radius in said chamber that is small comparedto the minimum significant size of said chamber;

(0) means for rapidly increasing the magnetic fiux within said chamber;and

(d) means for injecting electrons into said chamber during said increaseof magnetic flux at a rate sufiicient that the induced electric field ofsaid electrons is greater than the electric field produced by variationof said magnetic field, the mean direction of travel of said electronsbeing about said tubular axis and normal to both the induced electricfield of said electrons and said magnetic field.

10. In a direct current potential generator, the combination comprising:

(a) an evacuated tubular chamber having a tubular axis and closed onitself;

(b) means for providing in said chamber a magnetic field substantiallyeverywhere parallel to said tubular axis and having a strengthsuflicient to provide an electron gyro radius in said chamber that issmall compared to the minimum significant size of said chamber;

(0) means for rapidly increasing the magnetic flux within said chamber;

(d) means for injecting electrons into said chamber during said increaseof magnetic flux at a rate sufficient that the induced electric field ofsaid electrons is greater than the electric field produced by variationof said magnetic field, the mean direction of travel of said electronsbeing about said tubular axis and normal to both the induced electricfield of said electrons and said magnetic field; and

(e) means for injecting at least components of a gas into said evacuatedchamber.

11. The combination as defined in claim 10 wherein said components areions.

12. The combination as defined in claim 10 wherein said components areatoms.

13. In an electrical device, the combination comprising:

(a) an evacuated tubular chamber having a tubular axis and closed onitself;

(b) means comprising an electrical coil surrounding substantially all ofsaid chamber for providing in said chamber a magnetic field parallel tosaid tubular axis and having a strength sufiicient to provide anelectron gyro radius in said chamber that is small compared to theminimum significant size of said chamber;

(c) means for varying the magnetic flux within said chamber;

(d) means for injecting electrons into said chamber at a rate sufficientthat the induced electric field of said electrons is greater than theelectric field produced by variation of said magnetic field, the meandirection of travel of said electrons being about said tubular axis; and

(e) means for injecting a gas into said evacuated chamber.

14. The method of generating electric fields comprising the steps of:

(a) providing in an evacuated environment having a tubular axis amagnetic field comprising magnetic lines of flux substantiallyeverywhere parallel to said tubular axis and having a strengthsuflicient to provide an electron gyro radius in said envoronment thatis small compared to the diameter of said environment;

(b) rapidly increasing the lines of flux enclosed by said evacuatedenvironment; and

(c) injecting electrons into said magnetic field during said increase ofmagnetic flux at a rate to generate an induced electric field due tosaid electrons that is greater than the electric field produced by saidincreasing magnetic field, the mean direction of travel of saidelectrons being about said tubular axis and normal to both the inducedelectric field of said electrons and said magnetic field.

15. The method of generating electric fields comprising the steps of:

(a) providing in an evacuated environment having a tubular axis amagnetic field comprising magnetic lines of flux substantiallyeverywhere parallel to said tubular axis and having a strengthsufiicient to provide an electron gyro radius in said environment thatis small compared to the diameter of said environment;

3,441,756 9 10 (b) rapidly increasing the lines of flux enclosed by said17. The method of generating electric fields comprising evacuatedenvironment; the steps of: (c) injecting electrons into said magneticfield during (a) providing in an evacuated environment having a saidincrease of magnetic flux at a rate to generate an induced electricfield due to said electrons that tubular axis a magnetic fieldcomprising magnetic lines of flux substantially everywhere parallel tosaid is greater than the electric field produced by said tubular axisand having a strength sufficient to provarying magnetic field, the meandirection of travel vide an electron gyro radius in said environmentthat of said electrons being about said tubular axis and is smallcompared to the diameter of said environnormal to both the inducedelectric field of said elece trons nd aid magnetic fi 1d;and (b) rapidlyincreasing the lines of flux enclosed by said evacuated environment;

(d) providing ions in said magnetic field.

(c) injecting electrons into said magnetic field during 16. The methodof generating electric fields comprising the steps of: said increase ofmagnetic flux at a rate to generate (a) providing in an evacuatedenvironment having a, an induced electric field due to said electronsthat is tubular axis a magnetic field comprising magnetic greater thaf}the electric field Produced by Said ylines of flux substantiallyeverywhere parallel to said magnetlc l the mean direction of travel oftubular axis and having a strength sufficient to sa1d electrons beingabout said tubular axis and norvide an electron gyro radius in saidenvironment that mal to bot}? the mdllced elecmc field of sa1d elecissmall compared to the diameter of said environtrons arida1dmagnencfield; and menu (d) permlttmg electrons to flow through an electrical py increasing the number of lines of flux em load coupled across sa1dinduced electric field.

closed by said evacuated environment;

(c) injecting electrons into said magnetic field during said increase ofmagnetic flux at a rate to generate References Cited UNITED STATESPATENTS an induced electric field due to said electrons that g 7- isgreater than the electric field produced by said {ex er e a varyingmagnetic field, the mean direction of travel 3304463 2/1967 Wllbur3315-39 of said electrons being about said tubular axis and normal toboth the induced electric field of said elec- DAVID Primary Examinertrons and said magnetic field; and US. Cl. X.R.

(d) injecting a gas into said magnetic field. 3 13 157

